Unmanned Aerial Vehicles (UAVs) have been around for many years. Remotely controlled aircraft have been in use by both the military as well as civilian hobbyists for years. Many of these were of the traditional ‘fixed wing’ design, e.g. radio controlled (RC) model aircraft. More recently, small rotary wing craft, particularly multi-rotor craft (e.g. ‘quad copters’) have become popular in part due to their ease of operation and price point. This latter variant of UAV is commonly referred to as ‘drones’ although the class known as UAV properly defines a much larger variety of vehicles.
These UAVs or drones come in a wide variety of sizes and sophistication ranging from professional and military UAVs with navigation guidance and control systems, some as sophisticated as any manned aircraft and powered by turbine engines, to moderately sophisticated UAVs for limited commercial purposes, to small personal or recreational vehicles used primarily by hobbyists. The applicability of the present invention is to this latter category of vehicles. As applied to the present invention, the term UAV is intended to cover not only the hobbyist drones but also RC model aircraft, model rockets and even kites.
Recreational drones have captured the interest and imagination of the general public much in the same way as earlier generations were captivated by the introductions of remote controlled (RC) model aircraft and model rocketry during the space race. The speed with which these small recreational drones were introduced into the public domain exceeded the speed with which the US aviation regulators could promulgate regulations. That has begun to change and the Federal Aviation Administration (FAA) has recently issued rules governing UAV operations in the United States. Similarly the European Aviation Safety Agency (EASA) has begun issuing rules for UAV operation in Europe. It is of the utmost importance for recreational operators to follow these rules for both the safety of the public and their own wellbeing not to mention the long term viability of the hobby (one serious incident could well bring a halt to the hobby).
One of the most important factors in flying safely is the maintenance of a safe altitude. This is just as true with UAVs as it is with manned aircraft. Thus it is no surprise that one of the first regulations implemented by the FAA in connection with civil UAVs was regarding altitude.
By FAA regulation, drone operators must keep the flying vehicle less than 400 feet above ground level (AGL) (14 CFR .sctn. 107.51(b)). There is also a requirement that UAV operators (FAA.sctn. 107 refers to them as ‘remote pilots’) must maintain the UAV within visual line of sight (VLOS). Depending on the size of the UAV, maintaining VLOS of the UAV might be a more restrictive requirement than the AGL altitude requirement. Nonetheless, it is good situational awareness for the remote pilot to know the UAV altitude at all times. Also, there are often non-regulatory reasons why knowledge of the vehicle's current altitude is desired such as when doing photography or remote sensing operations and of course there is always just curiosity, ‘I wonder how high that thing is?’ Notwithstanding this need for constant vigilance of the UAV's altitude, there is currently a lack of availability in the market for an apparatus and method of measuring and monitoring the altitude of smaller UAVs. As understood in the art, ‘small’ UAV is meant to be a UAV weighing less than 55 lbs (14 CFR 107.3).
As mentioned, professional UAVs have sophisticated navigational and guidance systems which constantly measure and report altitude to a remote pilot, sometimes thousands of miles away. Additionally, many of the larger and more expensive recreational drones have an altitude monitoring capability built in as part of the drone's overall navigation and guidance and control module. Since the sensors and other components are integral to these UAV navigation systems, these altitude monitoring systems cannot be adapted for use on other smaller UAVs which do not come equipped with such capabilities. Furthermore, since the altitude sensor is only one component of a larger integrated navigation system, it would not be physically or functionally possible to place it on another UAV.
At the smaller end of the spectrum, UAV hand controllers (FAA term ‘control station’) generally do not include any altitude or other navigation monitoring function, they are strictly designed to provide flight control of the propeller motors and perhaps a small on-board camera. Nonetheless, these smaller drones are still subject to the same altitude regulations as their larger and more expensive brethren. Thus there is a need in the market to provide a real-time apparatus and method of monitoring the altitude of these smaller UAVs. Furthermore, an apparatus which can be removably attached to the UAV facilitates its use on several different models. Since hobbyists are known to frequently collect a stable of models, this allows the cost of the unit to be spread over an ever increasing heard.
Current aftermarket stand-alone devices which measure altitude for smaller UAVs do not provide a real-time, remote indication of altitude. For example, prior devices had been devised which capture altitude during flight but preserve only the highest value. Other devices which acquire a continuous report of altitude, do not transmit the data back to the UAV pilot in real-time but rather require a post flight visual inspection of the sensor or a download of its data. Thus, a remote pilot would know he violated altitude limits only after the UAV was on the ground and the post flight analysis had occurred, hardly useful for compliance. Furthermore, many of these devices utilize raw mean sea level (MSL) altitude data from the sensor uncorrected for local pressure setting. Thus conversion to the FAA's above ground level (AGL) altitude frame of reference requires both a correction for flight-time local pressure as well as knowledge of the operating location's MSL elevation. (As is well understood by those in the art, above ground level (AGL) altitude refers the height above the ground over which the vehicle is currently flying, mean sea level altitude (MSL) refers to the height of the vehicle above the mean sea level of the earth. AGL altitude may be computed by subtracting the elevation of ground level from the measured MSL vehicle altitude.) Thus continuous mental computation would be required to obtain a value useful to the pilot. Clearly these limitations are unacceptable when it comes to regulatory compliance and safety. To maintain safe situational awareness, the UAV AGL altitude must be known continuously and in real-time as the flight is underway.
Thus, what is needed is a small, stand-alone altitude monitoring system which can continuously transmit a small UAV's altitude and/or other flight data back to the remote pilot on the ground giving him/her a real-time indication of the UAVs altitude and/or other flight data and in the case of altitude data, preferably in AGL terms. The design of such a system would allow it to be easily removed and reattached to different UAVs. An additional goal is to have the airborne sensor system work with existing portable smart devices such as smartphones, smartwatches, tablet computers and the like.
In the context of this disclosure, ‘real-time’ shall mean that acquisition, processing, transmission, reception and display of the UAV altitude and/or other flight data, should occur with minimal perceptible delay between data acquisition and its display to the remote pilot. Further in the context of this disclosure, ‘stand-alone’ shall refer to a system which is not integrated physically or electronically into the original UAV system but rather something that is physically independent of the UAV airframe and hand controller and associated circuitry, which is capable of being operated independently of the UAV and which most likely is obtained in the aftermarket. ‘Removably attachable’ shall refer to a system which may be readily attached and detached from the UAV. Some examples of attachment means in this context would be using Velcro®, straps, clips, Scotch® mounting putty or restickable strips, Glue Dots®, ties, rubber bands, even tape or the like to name just a few, and would preclude attachments wherein the sensor is integrated into other UAV electronics. ‘Remote’ shall refer to the non-negligible physical distance between the UAV and the UAV pilot (‘remote pilot’) and/or the distance between the altitude sensor/UAV and the receiver/display (‘remote receiver/display’). For the purposes of this disclosure, the terms ‘sensed’ or ‘measured’ will refer to the data provided directly from the sensor while the terms ‘computed’ or ‘converted’ shall refer to the data resulting from some mathematical processing of the ‘sensed’ or ‘measured’ sensor value. One such example is that where the measured MSL altitude is converted to AGL altitude by application of a conversion factor. In an exemplary embodiment, this conversion factor is an altitude bias which is applied to the measured MSL altitude. In one example, this value is referred to as ‘zero_AGL_altitude_bias’ which is subtracted from the measured value. Determination of the ‘zero_AGL_altitude_bias’ is described below in detail.